This application is based on, and incorporates herein be reference, Japanese Patent Application No. 2001-86819 filed on Mar. 26, 2001.
1. Field of the Invention
The present invention relates to a solenoid valve. Particularly, the invention relates to an electromagnetic type oil control valve capable of switching between an advance and a retard chamber in a variable valve timing mechanism. The variable valve timing mechanism functions to change the timing of an intake or exhaust valve of, for example, an internal combustion engine.
2. Description of Related Art
Shown in FIGS. 6 and 7 is a related art electromagnetic type oil control valve 100 comprising a sleeve 105, a spool 106, a spring 107 for urging the spool 106 rightwards (with reference to FIG. 6), and an electromagnetic drive unit 109 for changing a position of the spool 106. The sleeve 105 has an opening 101 connected to an oil path formed on an oil pump side, an opening 102 connected to an oil path formed on a retard chamber side in a continuously variable valve timing mechanism, an opening 103 connected to an oil path formed on an advance chamber side in the continuously variable valve timing mechanism, and an opening 104 connected to an oil path formed on a drain side. The spool 106 has concavities and convexities corresponding to the openings 101-104.
The electromagnetic drive unit 109 is provided with an electromagnetic coil 112 wound around an outer periphery of a coil bobbin 111, a plunger 114 adapted to move integrally with a shaft 113, and a plunger guide 117 disposed between a stator core 115 and a yoke 116. In the electromagnetic type oil control valve 100, the plunger 114 is allowed to move linearly caused by an attracting force of the electromagnetic coil 112. The power thereof is used to move the spool 106 disposed within the sleeve 105, thereby switching the supply of oil to the retard chamber or the advance chamber, the supply of oil being from the oil pump to the continuously variable valve timing mechanism.
In the related art, supplying oil from the oil pump to the electromagnetic oil control valve 100 may be performed by the opening 101 formed in the side face of the sleeve 105. However, in machining the engine block, when the oil path from the oil pump is to be machined, complicated machining is sometimes necessary. This machining is sometimes necessary to fill holes after drilling in multiple directions in order to avoid interference with other oil paths, etc.
The machinability can be improved by using a single-drain hollow spool valve type solenoid valve and switching the arrangement of a partitioning portion between the oil pump side and the drain side, thereby allowing the opening connected to the oil pump-side oil path to be moved to the front end of the electromagnetic type oil control valve. However, since the pump pressure is applied to the interior of the oil control valve, higher strength is required for each component. In particular, to the plunger guide 117, as shown in FIGS. 6 and 7, since thin-walled stainless steel permits the improvement of magnetic efficiency, there arises the problem that if the plate thickness of the plunger guide 117 is increased for the purpose of improving its strength, a lower magnetic efficiency will result.
If an electromagnetic type oil control valve 100 of a side face oil supply type is used as the foregoing electromagnetic oil control valve of the front end face oil supply type, the opening connected to the drain-side oil path will open earlier than the opening connected to the oil pump-side oil path. There arises the problem that a vane rotor in the continuously variable valve timing mechanism will not be held steady, thus leading to a malfunction of the continuously variable valve timing mechanism.
It is an object of the present invention to improve the machinability of a feed path forming member by changing a feed position of a fluid or oil source. It is another object of the present invention to provide a non-magnetic member capable of attaining both improvement of pressure resistance and retention of magnetic efficiency. It is yet another object of the present invention to hold steady a vane rotor in a variable valve timing mechanism by opening an oil path on an oil source side earlier than an oil path on a drain side.
In one aspect of the present invention there is provided a solenoid valve wherein a feed port connected to a fluid flow path on a fluid source side is formed in one axial end face of a sleeve, while a discharge port connected to a drain-side fluid flow path is formed in the side face of the sleeve. A fluid pressure from the fluid source is applied to the whole of the interior of the solenoid valve. Particularly, the fluid pressure from the fluid source is applied to the bottom of a non-magnetic member which axially supports a movable member. By forming the bottom of the non-magnetic member with a curved shape so as to expand to the side opposite to the feed port side, it is possible to relieve stress concentration(s) on the bottom of the non-magnetic member. Consequently, the fluid pressure resistance of the solenoid valve can be improved without increasing the plate thickness of the non-magnetic member, and thus there is no fear of lowering the magnetic efficiency.
In another aspect of the present invention, the fluid flow path on the fluid source side is formed in a fluid flow path forming member formed coaxially with a solenoid valve mounting hole. Therefore, it is possible to decrease the number of machining steps for a feed path forming member. In a further aspect of the present invention, an inner periphery of a sleeve is formed with a contact surface for contact with an outer periphery of a hollow spool, whereby it is possible to prevent locking and wear caused by engagement of the sleeve with the hollow spool. In yet another aspect of the present invention, side corner portions for forming a concave fluid passage to provide communication between first and second openings and a discharge port are formed on the outer periphery of the hollow spool and are chamfered, whereby the flow of fluid can be stabilized and it is possible to improve control and stability of the system.
In still yet another aspect of the present invention, a side face feed valve is provided for feeding oil sideways from an oil source to a front end face feed valve for feeding oil from an axial front end face to a discharge port connected to a drain-side oil path. Additionally, a sleeve and a hollow sleeve are designed such that oil is fed into a retard chamber in a variable valve timing mechanism to let a first opening become larger than a second opening in a retarding operation involving draining oil present in an advance chamber in the variable valve timing mechanism. Additionally, the oil of the oil source is fed into the advance chamber to let the second opening become larger than the first opening in an advancing operation involving draining oil present in the retard chamber. According to this configuration, the first and second openings on the oil source side open earlier than the first and second openings on the drain side, so that the oil pressure from the oil source is constantly applied to the retard chamber or the advance chamber in the variable valve timing mechanism. Therefore, the operation of a vane rotor in the mechanism becomes stable.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.